Okay so I just finished swapping out the peanut cam in my 305 tbi for an LT1 cam. Also did shorty headers and full exhaust, no cat and an 80 series flowmaster. Replaced plugs and wires as well and the dizzy looked fine. I am having an issue with the timing. It seems that no matter how i turn the distributor (advanced or retarded) it backfires under light throttle at low rpm. I have been doing the "drive and tweak" method for about a week and can't seem to get it to go away. And the firing order is definitely correct. Help!

 

TBI needs to be set at 0 degrees. There is no "adjustment" - the computer takes care of that.

Generally speaking, for fuel injected applications, you need to tune the computer for all this additional airflow. Have you got a chip tuned for these changes? If not, I would contact TunedPerformance here on the forum and see what he can do for you. It's typically not expensive to get the right tuning.

GD

 

I have not done any chip tuning. I unfortunately had no luck searching for TunedPerformance also

 

The computer does not "take care of" ANYTHING.

All it does, is apply an OFFSET to wherever you crank the dist; JUST LIKE mechanical distributors. The only difference is, if the ECM hears spark knock from the sensor, it yanks about 50° of advance back out. Other than that, it works EXACTLY LIKE springs & weights: under any given conditions of RPMs, load (vacuum), etc., it just adds x number of ° to whatever pulse it gets from the pickup coil. Quite crude.

You need a tune. That part of the above advice is SPOT ON. What you have done, is DRAMATICALLY change the engine's airflow vs load curve, which needs to be matched with a totally revamped fuel vs airflow curve. It will NEVER run right without that type of change. Back in the day we'd do that sort of thing with jets, power valves, springs & weights in the dist, and all such as that; with EFI though, your ONLY option, is a tune. And not an "off-the-shelf" "chip" like Hypertech or the like, although you might accidentally get lucky; you need your fuel & spark curves matched to the "custom" engine you have created. Your engine isn't particularly unusual though, it might be possible to tell somebody who has already tuned a similar combo what you've got, and their tune might work or at least be real close, to where it can be readily modified; or, they may be able to develop what you need from data logging your car; or, they might just be real good at guessing. Feeling lucky today?

TunedPerformance is a user on this site that does tuning. Search this site for his userID.

You might also want to check out the EBL. http://www.dynamicefi.com/ Visit the DIY PROM board on this forum for suggestions on both that and various alternatives.

 

I simply meant that trying to find a spot where it will run correctly by turning the distributor isn't going to work. The computer must be tuned for correct spark advance and it expects whatever you programmed into it to be where you install the distributor. Which is 0 degrees for stock TBI. In other words there is not manual adjustment unless you first tell the computer what it's new base timing is supposed to be.

You must ask the ECM before making these changes. Twirling the disty *****-nilly will get you nowhere in a hurry.

GD

 

You can set an electronic dist ANYWHERE YOU WANT. Same as a mech one.

If you set it to 0°, and the ECM's table calls for 24° of advance, the final # will be 24° advance. If you set it to 4° BTDC and the ECM's table calls for the same 24°, the end result will be 28°. if you set it to 20° the end result will be 44°. It's no different in that regard from a mech dist: the ECM has not the vaguest foggiest dimmest remotest hint of a whiff of a glimpse of a clue where the crank and cam are at any given moment any more than the mech one does, other than the knock sensor; all it knows is, "pulse now".

Twisting the dist will produce EXACTLY the same results as a mech dist, for EXACTLY the same reasons, since they ultimately work EXACTLY the same way. This will include both good and bad results. Except that the bad results will take a different form: in the case of the mech dist and twisting it too much, it will ping or maybe even detonate; but in the case of the electronic, it will yank some YUUUUUJJJJE amount of timing back out as soon as it hears a knock. Safer, but more brutal in terms of performance.

That said, EXACTLY like a mech dist, if the CURVE is wrong, then the only cure is to tune it. A mech dist's curve is tuned with springs weights cams and cans where an electronic one is tuned by tweeeeeking the tables. But in the end, the effect of twiddling the dist body is all but IDENTICAL, subject to the above... it's all still compression, gasoline, and spark. Nothing changes no matter what the control system is. A "perfectly" tuned mech dist on your engine and an equally "perfectly" tuned electronic one, will yield the same curve.

Yours needs tuning, just like all of ours all used to back in the 70s. It just needs to be accomplished by different methods. You can twiddle the dist body and maybe make it better (or worse), but in the end, it'll never be RIGHT without tuning.

 

I understand what you mean. And you are absolutely correct.

I guess I was trying to tell the gentleman that the computer and the distributor are designed to work in concert with one another and unless you have the ability to burn a chip you probably shouldn't mess with the timing because changing the ignition timing, as you pointed out, requires the ability to tune the computer as well as move the distributor if applicable.

GD

 

Thanks for all the info. Turns out when I set the pre load for the valves (cold), I had almost a full turn too much on each rocker Adjusted while the engine was running and it runs like a dream. Idles so smooth I forget it's running sometimes and exhaust not is much cleaner and no popping or pinging. As far as tuning goes, I went with a chip from tbichips.com. After talking with Brian it should do the trick for me. I plan on running this setup and having fun until it blows and sealing in a junkyard LS and making some real power

 

A chip from TBICHIPS.COM is an absolute waste of time and money.

 

I installed it yesterday and it made one neck of a difference. Worth it in my book.

 

When you adjust the timing I suggest you also reset the IAC Valve and adjust the Minimum Idle Speed.

Timing
Start car and idle until the car is at operating temp. Disconnect the EST wire, adjust timing, reconnect EST wire. Shut off car .

Setting minimum idle speed.
1)Jump the A to B terminal under the dash in the ALDL Terminal as seen below.
2)Turn the key on but do not start it
3)You should hear a slight ticking coming from the IACV.
4)What 45 seconds then unplug the IACV with the ignition still on.
5)Disconnect the EST wire and remove the jumper.
6)Start the car.
It may be necessary to hold the throttle open slightly to prevent the engine from stalling.
Allow the engine to reach normal operating temperature.
7)Connect a tachometer. I used a digital timing gun with RPM feature.
8) Adjust the minimum idle speed using the throttle stop screw.
9) My Chilton’s says set it to 700rpm in park on an 89 TBI 5.0 auto.
10) When done shut the car off and reconnect the EST wire.
11) Plug the IACV back in.

Take it easy on the car for the first day or so.
Drive it normally on the street and highway to allow the ECM to re learn the new parameters.
The car will feel better and better as you do this.